Feat: Schema datatypes validation by pydantic

[mtovts]

A little suggestion for type checking in the Schema: Looks like it is a task for pydantic in input. This is more obvious and allows to reduce test cases.

[codecov]

Codecov Report

Merging #478 (b8d0aba) into main (75c69f0) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main      #478   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           47        48    +1     
  Lines         1588      1596    +8     
=========================================
+ Hits          1588      1596    +8     

Impacted Files	Coverage Δ
...penapi_python_client/parser/properties/__init__.py	100.00% <100.00%> (ø)
openapi_python_client/schema/__init__.py	100.00% <100.00%> (ø)
openapi_python_client/schema/data_type.py	100.00% <100.00%> (ø)
...on_client/schema/openapi_schema_pydantic/schema.py	100.00% <100.00%> (ø)

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[mtovts]

Returned tests for bad properties/additional_properties. Firstly thought it is about types. Now, instead of bad types, non-existent references are used.

[dbanty]

This is a great change, definitely improves the clarity of what's expected. Just would like to still point at 3.0.3 spec since we don't support 3.1.0 yet.